Influence of Non-equilibrium Conditions on Liquid Hydrogen Storage Tank Behavior

In  a  liquid  hydrogen  storage  tank,  hydrogen  vapor  exists  above  the  cryogenic  liquid.  A  common modeling  assumption  of  a  liquid  hydrogen  tank  is  thermodynamic  equilibrium. However,  this assumption may not hold in all conditions. A non-equilibrium storage tank with a pressure relief valve and a burst disc in parallel was modeled in this work. The model includes different boiling regimes to handle scenarios with high heat transfer. The model was first validated with a scenario where normal boil-off from an unused tank was compared to experimental data. Then, four abnormal tank scenarios were explored: a loss of vacuum in the insulation layer, a high ambient temperature (to simulate an engulfing fire), a high ambient temperature with a simultaneous loss of vacuum, and high conduction through the insulation layer. The burst disc of the tank opened only in the cases with extreme heat transfer to the tank (i.e., fire with a loss of vacuum and high insulation conductivity), quickly releasing the hydrogen. In the cases with only a loss of vacuum or only external heat from fire, the pressure relief valve on the tank managed to moderate the pressure below the burst disc activation pressure. The high insulation conductivity case highlights differences between the equilibrium and non-equilibrium tank models. The mass loss from the tank through the burst disc is slower using a non-equilibrium model because mass transfer from the liquid to gas phase within the tank becomes limiting. The implications of this model and how it can be used to help inform safety codes and standards are discussed.